The molecular basis of the progression of human prostate cancer toward its androgen-independent (AI) state is poorly understood. To address this question, our laboratory has developed a human prostate cancer model in which a prostate-specific antigen (PSA)-secreting human prostate carcinoma cell line, LNCaP, was coinoculated with a nontumorigenic human bone stromal cell line, MS into male athymic mice subcutaneously. The coinoculated cell populations interacted reciprocally and formed carcinoma. Recently, I have extended these observations and found that the induced prostate tumors when maintained in the castrated hosts underwent marked phenotypic changes, which associated with the appearance of the AI prostate cancer (i.e., rebound of serum PSA in the absence of androgen). At the molecular level, I have observed that the overexpression of androgen-upregulated gene (such as PSA), uncoupling from androgen control, was detected in AI tumors which accompanied with the increase in several androgen-repressed genes such as epidermal growth factor receptor (EGFR) and fibronectin (FN) genes. LNCaP subline derived from the AI tumors became tumorigenic when inoculated alone in nude mice and produced the prostate-specific autocrine factor (PSAF) which is capable of inducing PSA overexpression. Our preliminary data indicate that the synthesis and secretion of PSAF by the AI LNCaP subline is a part of the autonomous function of the cells and such function may be repressed by androgen. We have observed similar PSAF activity can also be detected in bone marrow aspirates obtained from prostate cancer patients with bony metastasis. Based on these observations, we hypothesize that the aberrant expression of androgen-repressed genes such as PSAF, EGFR and FN may play a key role in the autonomous growth of AI prostate cancer. To address these questions, the objectives of my proposal are: First, to isolate and characterize the PSAF from LNCaP subline and bone marrow specimens and clone the corresponding cDNA sequence. Also, to determine the molecular mechanisms of PSA gene expression in the presence of PSAF. Secondly, to investigate the function role of PSAF, EGFR and FN, and possible interaction among these genes in the AI progression of prostate cancer. I hope to focus my effort on the elucidation of molecular mechanisms associated with prostate cancer progression from androgen-dependent (AD) to AI state. Further exploration and understanding of the molecular and cellular events associated with the transition from AD to AI will aid future development of new therapeutic approaches to the treatment of human prostate cancer.